1. Field of the Invention
The present invention relates generally to an extensible lifting spreader frame for handling cargo containers.
2. Description of the Prior Art
Container handling spreader frames for attachment to an overhead crane or to lift trucks for handling containerized loads are well known. Typically, such prior spreader frames lift and handle cargo containers either from the bottom, using grappling arms attached to the frame, as exemplified by Whiteman U.S. Pat. No. R. 27,905, or from the top using hook-type latching devices carried by the frame, which interengage sockets at the four top corners of a container, as exemplified by Durenec U.S. Pat. No. 3,888,536.
Containers which are handled by spreader frames typically are of constant width and of one of two standard lengths, twenty- and forty-foot. Therefore, it is also common to provide extensible spreader frames which can handle both twenty-foot and forty-foot containers. Typical of such extensible spreader frames are those shown in the aforementioned U.S. Pat. No. R. 27,905; Zweifel et al U.S. pat. No. 3,514,146; Gottlieb et al U.S. Pat. No. 3,863,970; and Allegri U.S. Pat. No. 3,750,814.
One drawback of prior extensible spreader frames is their great weight, complexity and cost. These disadvantages have come about largely because such frames have incorporated power-operated means for extending and retracting them and additional power-operated means for operating their twist-lock latching mechanisms and grappling arms, if any. Furthermore, in the case of crane-suspended frames, such frames have also carried their own power sources, as exemplified by the aforementioned U.S. Pat. Nos. 3,514,146 and 3,888,536. As a consequence, most spreader frames have been of heavy, cumbersome, open rectangular frame construction typified by all of the aforementioned patents, and also by U.S. Pat. Nos. 3,863,970 and 3,712,661.
One exception to the typical rectangular open frame construction of spreader frames is the spreader frame shown in U.S. Pat. No. 3,750,814. Such frame is of generally telescoping single-beam construction with cross beams at the outer ends of the extensible telescoping beams. However, such frame is designed only for use by a forklift truck and, like other typical frames, employs power-operated frame extension means and power-operated container latching hooks. Accordingly, such beam-type frame is still heavy and costly to manufacture, and is suitable only for use with large, heavy duty lift trucks having an available source of hydraulic pressure fluid for the power-operated devices on the frame.